February 1 , 2012

SUBJECT: Canon EOS 5D Mark II, 7D and 1D Mark IV Image Quality Comparison in a Focal-Length-Limited Scenario -- Part I of II

I have thought long and hard about posting this because there's nothing that will raise a photographer's ire more than claiming a certain model camera is better than another. You might as well be comparing religions!

It got so heated on one of the forums, that I was accused of being chained to a tree. Here's a direct quote:

"A competent bird photographer does not chain themselves to a tree and photograph a far subject and then try to crop the image. Heavy crops and framing noisy pixels is the number 1 reason for those lousy IQ images that we often see posted. To think bird photography is generally "focal length limited" is ridiculous IMO and it indicates a short coming on the photographer side. If the birds are too far and you can't get close enough you should not waste those electrons taking a picture at first place.."


I do agree that there is a limit to how much you can crop an image before the quality suffers, but there's plenty of instances in which images are cropped in post processing to frame the bird pleasingly. How often do you crop an image of a bird? I do it the majority of the time.

To set the stage of my test, I must explain my frustration with camera comparisons commonly found on the Internet and in magazines. In all cases that I have found, their tests are conducted by either zooming in/out or physically moving the camera closer/further to their test panels to frame the test panel identically. Although these tests are valid for a portrait photographer, they are not complete. They are not valid for situations in which the photographer is focal-length-limited.

So what does focal-length-limited mean?
Simply put, it means that the photographer must take an image from a set distance. Moving closer or further from the subject is not possible. Here are a few examples:

--> Photographing the moon.

--> Photographing a bird-in-flight.

--> Photographing a warbler near the top of a tree.

--> Photographing from a blind.

--> Photographing a bird located on private property.

--> Photographing water fowl from shore.

I think you get the idea. Of course there are times in which you can move closer. A good example of this are the many tame birds found in Florida...It's a bird photographer's paradise down there!

In conclusion to my argument that bird photographer's are quite frequently focal-length-limited when photographing birds, I submit to you the following question:

If we are not focal-length-limited when photographing birds, why are there so many photographers with 500mm, 600mm and 800mm lenses using teleconverters to increase the focal length to 700mm, 840mm and beyond? If we were not focal-length-limited, would there be any reason to spend thousands of dollars to get closer to a bird? Most of the time we are wanting "more reach" because we are focal-length-limited.

At least for myself, I am using a 600mm lens with a 1.4x teleconverter 75 to 80 percent of the time because I am looking to fill the frame as best as possible with a wild bird. And when I am photographing a bird at 840mm, there's usually plenty of room left in the frame for post-cropping. Which leads me to my next subject...

It is a very rare that a focal-length-limited image is not cropped in some form or fashion while post-processing. If I were a portrait photographer, the rules would be different, but typically when photographing birds, we crop the image to frame the bird pleasingly and/or to bring out the details of the bird.

I also crop the image typically to 300 dpi. I use this as a rule of thumb because quite often when asked by a publisher for an image, their request is almost always for 300 dpi images. Depending which camera I am using, this may mean the image is downscaled (pixels are discarded) or upscaled (pixels are added) while cropping the image.

As part of my image quality comparison test, I cropped all images. At least for my post-processing workflow, it is what I normally do and selfishly, this test (originally) was for my own benefit.

Some of you may argue that this invalidates the test. I agree that this could skew the results if I am downscaling. So when doing this comparison, I made sure that all images were upscaled so that no data was lost. I did so by changing the dpi to 400. In all instances pixels were added and not discarded.

The Great Equalizer
Here's the kicker to the whole test. Each camera used in this test has a different sensor size. The 5D Mark II has a full-frame sensor meaning that its size is about the same as a piece of 35mm film. Typically, these full-frame camera bodies have larger size pixels since the sensor is relatively large. This reduces the signal-to-noise ratio of the sensor which creates incredibly low-noise images when you do not need to post-crop the image. Next in the bunch is the 1D Mark IV which has a 1.3x cropped sensor (smaller) followed by the 7D which is a 1.6x cropped sensor (smallest).

Now let's say I am photographing a bird from a set distance and I am able to photograph the bird through the same lens with all three cameras. If I were to superimpose all three images made from the different camera bodies, I would see something like this:

As shown above, the field-of-view for all three of these cameras are quite different. Now if I were to take all three images and crop them identically to show the same field-of-view, we could state the following:

The full-frame sensor camera would receive substantial cropping. The 1.3x camera would receive a moderate amount of cropping. The 1.6x camera would receive very little cropping.

We can also state:

The greater an image is cropped, the greater the image will be degraded by noise and pixelization caused by upscaling.

This is the great equalizer when comparing different sensor size cameras. But remember, this only applies to focal-length-limited scenarios.

Test results to follow in Part II...


—Alan Stankevitz




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